Galvanized steel sheets are relatively inexpensive, and also excellent in rust resistance. Thus, the sheets are used in many fields of automobiles, architecture and construction materials, electronic products, and others.
Regarding a galvanized steel sheet, the coating weight (the amount of deposit per unit area) of its galvanization is varied in accordance with a use field thereof. However, even when the coating weight is varied, gas metal arc welding (GMAW) using a solid wire is used for welding the galvanized steel sheet in many cases. In particular, in the field of automobiles, the GMAW is very frequently used.
Although galvanized steel sheets have the above-mentioned advantages (low costs and rust resistance), it cannot be said that the sheets are excellent in weldability when a solid wire is used to subject the sheets to gas metal arc welding. It is known that many porosity defects such as pits and blowholes, and spatters are generated.
A cause that galvanized steel sheets are not excellent in weldability as described above would be that the boiling point of zinc is largely lower than that of iron. Specifically, in the state where iron of a galvanized steel sheet is melted while this sheet is being welded, its zinc is already in a gasified state to be present in the form of a vapor (zinc gas). As a result, the zinc gas generated from the molten pool remains in the molten pool, so that porosity defects such as pits or blowholes are generated. Moreover, the zinc gas jetted out from the molten pool disturbs the droplet transfer at the time of the welding, so that spatters are generated in a large amount.
Considering such a situation, various suggestions as described below are made regarding a solid wire in which the generation of porosity defects such as pits and blowholes is restrained, and spatters are decreased.
For example, JP 1101-143775 A suggests a welding method using a wire in which the content of each of Si and Mn is restrained within a predetermined value, and further using an Ar gas into which CO2 or O2 is incorporated in a predetermined proportion.
JP S63-242488 A and JP H04-135088 A each suggest a wire in which the content of each of Si and Mn is restrained within a predetermined value.
JP H07-80678 A suggests a wire in which the content of each of Si and Mn is restrained within a predetermined value, and Al and Ti are each incorporated in a predetermined proportion.
JP 2004-136342 A suggests a wire in which the content of each of Si, Mn and Cr is restrained within a predetermined value.